The present invention relates to a liquid level detection apparatus that has a pair of first electrodes and a pair of second electrodes to detect the level of a liquid in a container based on a capacitance between the first electrodes and a capacitance between the second electrodes.
It is known that a pair of electrodes develops a capacitance therebetween depending on the permittivity of a material around the electrodes. In view of such a known fact, there has been proposed a liquid level detection apparatus having a pair of electrodes to detect the level of a liquid based on a capacitance developed between the electrodes. Japanese Laid-Open Patent Publication No. 63-079016 discloses a liquid level detection apparatus of the proposed type, having a sensor that includes a pair of linear sensor electrodes, a pair of linear reference electrodes and a printed circuit board insulatively supporting thereon the sensor and reference electrodes. The sensor and reference electrodes are arranged at different height positions such that the whole of the reference electrodes and at least parts of the sensor electrodes are immersed in a test liquid. In this state, the liquid level detection apparatus measures a capacitance between the sensor electrodes and a capacitance between the reference electrodes, calculates a permittivity of the test liquid from the reference electrode capacitance, and then, determines a level of the test liquid based on the sensor electrode capacitance and the test liquid permittivity.